This invention relates to the measurement of steerable wheel geometry. More particularly the invention relates to a device and method for measuring the steering axis inclination of a steerable wheel, and in still greater particularity the invention relates to a device and method for expanding the capabilities of a caster-camber measuring gauge for measuring steering axis inclination.
Various devices have been devised for measuring the individual steerable wheel geometric relationships known as caster and camber. One such device to which the present invention applies is disclosed in U.S. Pat. Nos. 3,520,064 and 4,114,283. The latter patent discloses various improvements to the gauge of the former patent. The gauges disclosed in these patents, and in particular the gauge of U.S. Pat. No. 4,114,283, are compact, accurate, easy to use gauges. However, neither of these gauges are, in the absence of the invention disclosed herein, capable of measuring the relationship known as steering axis inclination. Steering axis inclination is the tilt of the spindle support arm along a vertical plane parallel to the spindle and perpendicular to a plane parallel with the wheel, and is an important relationship for proper operation of the vehicle in which the steerable wheel arrangement is utilized. In general, for modern applications, the steering axis inclination is a fixed non-adjustable relationship that either falls in or out of a predetermined range of permissible values. Normally, if after adjusting the variable relationships camber and caster, the steering axis inclination does not fall within the permissible range, there is an indication that structural damage to a steering member is present. Most often the damage is to the spindle support arm itself. Without means for measuring steering axis inclination, serious structural damage can go undetected resulting in improper operation of the vehicle, and in more extreme cases, the vehicle can be unsafe to operate.
Devices and methods for measuring the steering axis inclination exist, however they most often use sensitive and bulky optical and light projection systems that require fine and precise calibration, care and handling by service personnel. There is a need for a device and method that allows steering axis inclination to be measured easily, fast, accurately and with minimum manipulation of equipment by personnel.